Polyphase transformer



y 19-60 J. L. ANDERSON E'I'AL 2,946,028

POLYPHASE TRANSFORMER Filed April 12, 1954 3 Sheets-Sheet 1 )3 IINVENTORS.

- John L. firm arson James 6. Ever/747$ y 1960 J. L. ANDERSON ET AL2,946,028

POLYPHASE TRANSFORMER Filed April 12, 1954 3 Sheets-Sheet 2 INVENTORS.JB/m L. flnaerson James 6. Ever-hart BxPiLWZ W.

Filed April 12, 1954 r Uj IN V EN TORS. ohn 1. flndersan James 6.[yer/1dr: M ii. TV. 3 742mm POLYPHASE TRANSFORMER Filed Apr. 12, 1954,Ser. No. 422,374

'4 Claims. (Cl. 336-5) This invention relates to polyphase transformersand is particularly directed to the core construction.

This invention is an improvement on the transformer which forms thesubject matter of the Link Patent No. 2,431,128, granted November 18,1947, and assigned to the assignee of the subject invention. The coredisclosed in the Link patent comprises two inner, wound strip, closedcore loops mounted back to back and surrounded by an outer, closed coreloop wound from magnetic ribbon. The adjacent sides of the two innercore loops constitute the center winding leg while the outer sides ofthe inner core lops and the abutting sides of the outer core loopconstitute the two outer winding legs of the three phase core. In such acore, it is necessary for some of the flux to pass from loop to loop,but this is extremely difficult because the reluctance to flux travel ina direction perpenticular to the laminations is quite high. Thus, mostof the flux from the center winding leg cannot return through the entirecross section of the outer winding legs and is principally concentratedin the portions of the outer legs formed by the inner core loops.

An object of the invention is at provide a unitary magnetic core havingat least two distinct closed magnetic circuits of lengthwise bentlaminations interconnected by low reluctance iron paths to permit fluxtransfer between said circuits. 7

A further object of the invention is to provide a unitary,

multi-legged magnetic core in which all portions of the core areintegral and wound from magnetic strip which is continuous throughoutthe core.

Another object of the invention is to provide an improved three phasetransformer having an 8-shaped core of the wound strip type wherein itis unnecessary to rely completely on flux leakage through highreluctance air paths to interlink the inner and outer core loops andwherein these portions of the core are directly interlinked magneticallyby low reluctance iron paths.

Still another object of the invention is to provide an improved threephase transformer having a three legged, wound strip core wherein adirect iron path is provided for transfer of flux from the centerwinding leg to the outer core loop.

In accordance with the invention, the inner and outer loop portions ofthe core are magnetically interlinked by low reluctance iron pathspreferably having grain orientation in the direction of flux travel. Theouter loop portion is wound as a continuation of the magnetic ribbons ofthe inner loop portions to provide a direct iron path for transfer offlux between inner and outer loop portions. By means of thisconstruction, the flux from any winding leg has return paths includingthe entire cross section of the iron of the other winding legs.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appending claims.

'nited States Patent h" PatentedJuly 19, 1960 In the drawing 1 Fig. l isan elevation view of one embodiment of the invention;

Fig. 2 is an elevation view of an alternative embodiment which permitsmore efiicient flux transfer than the embodiment of Fig. 1; and

Fig. 3 is an elevation view of an alternative embodiment wherein aplurality of magnetic ribbons interlink each inner loop portion with theouter loop portion.

Referring to the drawing and more particularly to Fig.

' 1, it will be seen that the transformer core structure comprises twoinner loop portions indicated generally by the reference characters Aand B, and an outer continuation loop portion indicated generally by thereference character C surrounding the inner core portions A and B andWound from the magnetic ribbons of the inner loop portions. Each of theinner loop portions is formed by winding' a closed core of magneticribbon. Although any suitable magnetic ribbon may be utilized, it ispreferable to utilize silicon steel having a preferred orientation ofthe grain lengthwise of the direction of winding.

The inner loop portions A and B are both formed in an identical mannerand only portion A will be described. The parts of inner portion B aregiven the same reference numerals as those of inner portion A with theaddition of the prime designation. Although each inner loop portion maybe formed from a single continuous ribbon spirally wounnd fiatwise toprovide a rectangular cross section, inthe embodiment illustrated inFig. 1 various widths of strip are utilized to build upcruciform-in-crosssection inner loop portions A and B. A magnetic ribbonof suitable width is first spirally wound fiatwise to provide a closedcore section 10 of desired thickness. The principal novelty of theinvention resides in the provision of direct iron paths between innerand outer loop portions, and inasmuch as the inner two sections of theinner loops and the outer two sections of the outer loop of theembodiment of Figs. 1 and 2 are similar to prior art constructions, theconvolutions of these sections have been omitted from the drawing todirect attention to the principal novelty. The winding is preferably ona rectangular mandrel, although it is within the scope of the inventionto wind on a circular mandrel and thereafter shape the core section torectangular configuration. A magnetic ribbon of greater width is thenwound over the ribbon of the inner section 10 to form a closed coresection 11. Thereafter a magnetic ribbon 12 of still greater width iswound around the convolutions of the core section 11 to form a closedcore section 13. The ribbon 12 is not severed after the desired numberof turns have been Wound.

It is well known in the art that when the winding of a core section iscompleted, the outer end of the magnetic ribbon may be brazed, tackwelded, or otherwise secured as indicated by the reference numeral 14and further that the ends of successive magnetic ribbons may be joinedby welding or brazing, if desired. However, it has been their longersides abutting. The manner of mounting the inner loops A and B on acommon arbor does not constitute part of the present invention and isnot illustrated in the drawing. It is apparent that the rectangularmandnels (not shown) on which the loops A and B are originally wound canbe supported directly on the base which is then rotated to wind theouter core loop, or, if desired,

3 the inner portions A and B can be first removed from the rectangularmandrels before being mounted on the rotatable base.

The base (not shown) is then revolved to simultaneously rotate the twoinner loop portions A and B as an integral entity with their longersides abutting. Upon continued rotation of the base, a closed outer coresection 17 is spirally wound to the desired thickness surrounding theinner two core sections A and B with the two ribbons 12 and 12"inparallel in each spiral layer.

The number of laminations in a radial cross section through the finalcore may be in the hundreds, and the impossibility of illustrating allof the convolutions in the drawing is obvious. Consequently, thethickness of the magnetic strip is greatly exaggerated in the drawingand tends to give the impression that the joints between successivestrips would cause bulges in the core portions radially outwardtherefrom. However, when it is consider'ed that the thickness of theindividual convolutions is usually measured in thousandths of an inchand that such joints may be staggered peripherally, it will beappreciatcd that the joints do not appreciably affect the shape of thefinal core.

The next step is to wind a single narrower magnetic ribbon, ofapproximately the same width as the ribbons of sections 11 and 11, intoa closed core section 18 surrounding the core section 17. Here also theconvolutions of the section 18 are omitted from the drawing. The ends ofthe ribbons 12 and 12 are preferably staggered peripherally, and the endof the single magnetic strip from which the section 18 is wound may bebrazed, tack welded, or otherwise secured to one or both strips 12 and12, or may be joined thereto by slitting the magnetic ribbons near theirends across a portion of their width and dovetailing the slit portions.Thereafter, a narrow magnetic ribbon having a width approximately equalto that of the ribbons forming the core sections 10 and 10 is wound intoa closed core section 19 surrounding the section 18 and its end is tackwelded, brazed, or secured by a peripheral clamping band encircling theouter loop C.

It is to be noted that the three phase transformer has a central legformed by the abutting straight sides of the inner loops A and B and hastwo outer legs formed by the abutting outer straight sides of the innerloops A and B and the spaced straight sides of the outer loop C.

The entire core is then annealed so as to remove all stresses due to theworking of the magnetic ribbon during Winding. After annealing there isno further working, machining, or bending of any of the magnetic ribbonsand consequently there is no stress imparted to any portion of the corewhich would otherwise adversely affect the characteristics of thetransformer.

The conducting winding asemblies, or electrical coils, 20, 21 and 22,including primary and secondary windings, are wound on the finishedannealed core in any suitable manner, preferably by the apparatusdisclosed in the Patent 2,305,999 to Steinmayer et al. dated December22, 1942. The outer straight portion of the inner core loop A and theabutting straight portion of the outer core loop C pass through thewinding window of the electrical coil 20 to form one outer leg; theabutting back to back straight portions of the inner core loops A and Bpass through the winding window of the electrical coil 21 to form thecentral leg 15; and the outer straight portion of the inner core loop Band the abutting straight portion of the outer core loop C pass throughthe winding window of the electrical coil 22 to form theother outer leg.

After the conducting windings have been finished, suitable wedges 23 maybe driven in place as shown to suitably hold the electrical coilassemblies firmly positioned with reference to their winding legs.

In order to simplify the drawing and to facilitate the understanding ofthe invention, the electrical coil assemblies 20, 21 and 22 are omittedin Figs. 2 and 3 of the drawing. The embodiment f Fig. 2 is similar tothat of Fig. 1 except that a more efficient interlinkage of flux betweencore loops is obtained. Two inner core loops A.

and B, substantially identical to the inner loops A and B of theembodiment of Fig. l, are mounted on the rotatable base so that theirdirection of winding is the same (for example, counterclockwise) andwith the unsevered magnetic ribbons 25 and 26 from the outer sections 27and 28 of the inner loops A and B respectively extending from oppositeends of the central leg 29. The base is then rotated in the oppositedirection from that in which the inner core loops A and B were wound,i.e., clockwise, to spirally wind the two ribbons 25 and 26 .in parallelaround the inner loops A and B in order to construct the inner section30 of the outer loopC- The effect is that the magnetic ribbon from theouter section of each inner loop is wound in the reverse direction tocomplete a closed flux path around the other inner loop before thewinding of the outer loop C is initiated. The magnetic ribbon 25 of theouter section 27 of the inner loop A is illustrated as woundcounterclockwise with the outer laminar convolution 31 thereofseparating from the upper end of the central winding leg 29 whereindicated by the reference numeral 32. is then. continued in theopposite direction, i.e., clockwise, in a turn 33 around the inner loopB before the two ribbons 25 and 26 are paralleled and spirally woundtogether clockwise to form the inner core section 30 of the outer loopC.

The magnetic ribbon 26 of the outer section 28 of the inner loop B isshown as wound counterclockwise, and the outer laminar convolution 34separates from the lower end of the central winding leg 29 whereindicated by the reference numeral 35. The ribbon 26 is illustrated ascontinuing in a clockwise direction in a turn 36 around the inner loop Abefore the two ribbons 25 and 26 are paralleled and spirally woundclockwise together to form except that a plurality of magnetic ribbonsinterlink the inner and outer portions, or loops, of the core. innercore loops D and E are constructed in a manner similar to theembodiments of Figs. 1 and 2 except that instead of varying the width ofsuccessive strips to provide cruciform cross section, in order tosimplify the description and to aid in the understanding of the drawingthe embodiment of Fig. 3 is illustrated with constant wlidth magneticstrip throughout the core to obtain a radial cross section ofrectangular configuration. Each spiral turn comprises a plurality ofribbons in parallel, two parallel ribbons 40 being illustrated in eachconvolution in inner loop D and two parallel ribbons 40' in each.convolution in inner loop E. Although the exaggerated thickness of thelaminations permits the illustration of only two magnetic ribbons inparallel, it will be obvious that any desired'number of ribbons may beso wound to interl-ink the inner and outer loops. As in the embodimentof Fig. l, the ribbons 40 and 4d are not severed after the desirednumber of turns have been spirally wound to form the inner core loops Dand E. A

The two inner loops D. and E are then mounted on a rotatable base (notshown) with the free length of the uncut ribbons 40 and 40 continuoustherewith and with the straight portions of the longer legs abutting inthe manner described for the embodiment of Fig. l. Preferably the innerloops D and E are disposed on the base so that their direction ofwinding is the same andwith the uncut magnetic ribbons 40 and 40'extending from opposite ends of the central winding leg. After half arevolution of the rotatable base (not shown), the ribbons 40 and 40 ofthe two inner portions D and E are in parallel, and upon continuedrotation of the base, the ribbons The ribbon 25 Two 40 and 40 arespirally wound to tightly and closely embrace the abutting innerportions D and E. The four parallel ribbons 40 and 40' are continued toform a closed outer core loop F having approximately the same thicknessas the inner loops D and E. The ends of the magnetic ribbons 40 and 40are secured by brazing, welding, or by a peripheral clamping bandencircling the outer core loop F.

The invention provides a unitary polyphase transformer constructionwhich utilizes the wound core principle and in which the inner and outerportions, or loops, of the core are directly interlinked byferromagnetic paths. It is to be noted that there are no air gaps in themagnetic path and that low reluctance iron paths interlinking the innerand outer portions of the core have the grain of the magnetic ribbon inthe direction of flux travel. It will further be noted that a directiron path is provided for the flux of the middle winding phase, i.e.,the center winding leg, to transfer into and return from that portion ofthe outer winding legs formed by the outer loop of the core. The fluxfrom any winding phase can thus return through the entire cross sectionof the other winding legs without transferring through high reluctanceair paths perpendicular to the laminations as in three legged, threephase cores heretofore constructed.

Although the method of construction has been described as including themounting of two inner core loops as an integral entity on a rotatablebase to wind the outer loop, it will be appreciated that the methoddescribed is merely illustrative and that the disclosed transformer coreis capable of construction by other means, e.g., the outer core loop maybe wound manually, if desired. The description has been limited to athree legged, three phase transformer, but it will be appreciated thatthe invention comprehends any transformer of the type having lengthwisebent, concentrically stacked laminations wherein it is desirable tointerlink portions of the core with low reluctance iron paths.

While only three embodiments of the invention have been illustrated anddescribed, it will be obvious to those skilled in the art that changesand modifications can be made without departing from the invention, andtherefore it is intended in the appended claims to cover all suchchanges and modifications as fall within the true spirit and scope ofthe invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is: I

1. Three phase electromagnetic induction apparatus comprising threeelectrical coils each having a winding window and adapted to beconnected to one of the phases of a three phase electrical system and a.unitary magnetic core having a first loop portion spirally wound ofmagnetic strip material passing through the winding window of a firstand a second of said coils disposed adjacent each other and magneticallylinking said coils,

having a second loop portion spirally wound of magnetic strip materialpassing through the winding window of the second of said coils andthewinding window of a third of said coils which is disposed adjacentsaid second coil and magnetically interlinking said second and thirdcoils, and having a third loop portion spirally wound from magneticribbon continuous with the magnetic ribbon of said first and secondportions, said third portion passing through the winding window of saidfirst and third coils and magnetically interlinking said first and thirdcoils.

2. In a polyphase induction apparatus having three parallel, spacedapart, winding legs having a common central plane, a magnetic corestructure comprising a pair of inner loop portions each formed ofmagnetic material spirally wound flatwise, said inner loop portionshaving side portions adjacent each other forming the central one of thethree winding legs and having side portions remoted from each otherforming parts of the two outer winding legs, respectively, and an outerloop portion of spirally and flatwise wound magnetic strip materialextending about and enclosing said inner loop portions and forming partsof the two outer winding legs, the magnetic strip from theouterconvolution of both said inner loop portions being spirally wound inparallel about said inner loop portions to form at least the innerconvolution of said outer loop portion.

3. A unitary core construction for three phase transformers comprisingtwo inner, contacting, convoluted loop portions and an outer,convoluted, loop portion contacting the majr portion of the peripheriesof the inner loop portions, each loop portion consisting of magneticstrip material spirally wound flatwise, the arrangement being such thatthe inner loop portions jointly provide a central core leg and with theouter loop portions provide a pair of outer legs, at least the innerconvolution of said outer .loop portion being wound from the magneticstrip 0 both said inner loop portions. 4. A unitary core constructionfor'three phase transformers comprising two inner,substantiallyrectangular,

contacting portions and an outer substantially rectangu lar portionembracing the inner portions, the arr-angement being such that the innerportions jointly provide a central core leg and with the outer portionsprovide a pair of outer legs, said portions each consisting of y aplurality of convolutions of magnetic strip material spirally woundflatwise, at least the outer convolution of both said inner portionscomprising a plurality of magnetic strips in parallel and 'at least theinner convolution of said outer portion being wound from the magneticstrips ofthe outer convolution of both of said inner loop portions inparallel.

References Cited in the file of this patent UNITED STATES PATENTS2,382,172 Putman et al. Aug. 14, 1945 2,404,016 Wiegand July 16, 19462,408,212 Hodnette Sept. 24, 1946 2,431,128 Link Nov. 18, 1947 2,478,030Vienneau Aug. 2, 1949 2,479,391 Miller, Aug. 16, 1949 2,516,164 VienneauJuly 25, 1950 2,532,171 Kaini Nov. 28, 1950 V f FOREIGN PATENTS 640,618Great Britain July 26, 1950 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 946,028

John L, Anderson et a1a July l9 1960 It is hereby certified that errorappears in the printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

for "remoted" read Column 6, lines 12 and 13 read major a remote line 25for '"majr Signed and sealed this 27th day of December 1960a (SEAL)Attest:

KARL H. AXLINE Attesting Officer RoBEriT c. WArso'N Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,2346,0255

John L Anderson et alq July 19 1960 It is hereby certified that errorappears in the printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 6, lines 12 and l3, remote line 25 for 'majr for 'remoted" readread major Signed and sealed this 27th day of December 1960 (SEAL)Attest: v KARL H. AXLINE ROBERT c. WATSUN Commissioner of PatentsAttesting Oificer

